Magnetic fields are commonly used in the operation of electronic devices, for example, to accelerate and focus electrons in a free electron laser. Such magnetic fields are generated by large mass, current driven systems typically comprised of a solenoid, an external power source and a means for cooling the coils of the solenoid. The disadvantage of such conventional systems, however, is that they are large, expensive and use lots of energy.
The foregoing disadvantages are apparent when conventional electromagnetic apparatus are used to operate a free electron laser. A free electron laser typically has a passageway, often an excavated cylindrical space, through which an electron beam can pass. This passageway can be comprised of hard ferromagnetic material, i.e. magnets, or it can be an iron Chiron Wiggler. Chiron Wigglers are well known in the art. See R. H. Jackson et al., The Coaxial Hybrid Iron Wiggler, Nuclear Instrumentation Methods, Physics Research, Vol. A (1994). An externally mounted solenoid would be used to create an axial magnetic field along the length of the passageway. This axial field would then saturate the material comprising the passageway, i.e. iron, thereby inducing a transverse magnetic field that alternates in direction with displacement along the length of the passageway. This transverse field would accelerate and cause the electrons to oscillate circumferentially as they pass longitudinally along the passageway.
Accelerated electrons are known as wigglers. Wigglers radiate energy, the frequency of which depends on the strength and periodicity of the magnetic field. However, the radiation produced by an electron beam which oscillates in an alternating field is of a wave length commensurate with the period of the magnetic field, so that for short wavelengths it becomes difficult to space magnets of sufficient thinness to operate and attain sufficient field strength to accelerate the electrons. To some extent this "tyranny of size" can be overcome by use of relativistic electrons which "see" a magnet structure that shrinks with increasing electron energy. While such an arrangement works, it requires massive equipment to generate the high voltage needed to impart to the electrons enough energy to make them relativistic thereby frustrating the goals of compactness and lightness. The present invention addresses this problem of unattainably thin magnets by use of a permanent magnet structure which includes a Chiron Wiggler, to simultaneously generate sufficient field strength and sufficiently short periods.
It is, therefore, an object of the present invention to replace the actuating solenoids of conventional electromagnetic systems with a compact, light weight permanent magnet structure which includes a Chiron Wiggler, to provide the desired magnetic field, thereby eliminating dependence on electric currents and their power supplies.